This was a legal solution to a technical problem. If you can't fix the hardware, pass a law. Can you spell DMCA? Never mind that anybody can build/buy a simple converter that allows listening. Keeps the harmless people out of your business. Only people who could listen to your phone conversation were criminals, by definition.
Older, unblocked receivers are available. There are a bunch of early ham-radio handheld transceivers that are unblocked. mike
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GSM may or may not frequency-hop, depending on the network settings. GSM uses a narrow-band modulation scheme (GMSK) but if frequency hopping is enabled then it will use a different centre frequency for each burst. Error correcting codes are used to spread the information in a given block over multiple bursts, so that if a single frequency happens to be faded then you can still recreate the block.
For GSM at least, there is even some encryption on top of that, so that the restriction is particularly stupid. See the FCC Part 15 regulations section
15.121 though.Jonathan
Hi all,
I've been looking for a scanner to do some experiments and I got confused by the "Cell blocked" fine print. I don't really care to listen to cell phone conversations of any kind. I thought most cell modulations are either digital or code hoping or both. Only old cell phones could potentially be heard on a scanner. A professor in college said that cell phones frequency hop every 16 ms ( or so ). This is old info (hopefully reliable). So, I imagine the new stuff is really protected from a simple scanner ? Yet, all scanners sold in the USA are "cell blocked". Could someone shed some info on the subject ?
Thanks
by
on
"Cell blocking" dates back to the old analog systems, which are rare now but still used in places. Modern digital systems are not able to be eavesdropped on by the casual listener. AFAIK only the US mandates blocking of the frequency range commonly used by cell systems, so any coming from overseas could tune up to listen to white noise or other undecipherable garbage.
A CDMA system may hop frequency as often as you say, but others (GSM, D-AMPS, etc) don't. Their encoding algorithms provide enough content protection for scanners to be useless against them. CDMA doesn't do the hopping just to make them 'invisible' to scanners, of course, but that's a nice side effect.
Ken
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